Fed up with carrying large or bulky grey cards that get bent and creased or get dirty and fade? Why not try one of the great Lastolite pop up grey cards? I have the 30cm 18% grey pop-up grey card and it works really well. When folded it’s only about 12cm across so takes no space at all. It comes in a handy zip up case. This is so much easier to carry and transport than traditional ridged cards. The back of the target is 90% white. Both the grey and white targets appear to be very accurate and the matte surface of the grey card helps eliminate hot spots and reflections. There is a cross hair style focussing target in the center of each side if you need to check focus. They come in different sizes, if you want a larger one there are also 50cm and 75cm versions plus there is even an underwater version. Do note that they come in both 18% and 12% shades of grey. Really handy if shooting with SLog or for setting white balance. If you are working with a video camera you want the 18% grey version, but you may need the 12% version if calibrating a light meter etc. Simple, low cost item that works really well. Recommended!
http://www.lastolite.co.uk/ezybalance-grey-wht-card-03m-lllr1250